Using the PBEsol function of the GGA approximation of the DFT method included in the CASTEP program, the optimization of the geometric structure of MgO and CaO was calculated to observe the possible phase transformation of their crystal structures in a pressure range from 0 to 140 GPa. The evolution of the Debye temperature with pressure changes was also examined after calculating the elastic properties. We were therefore able to study the changes in heat capacity, internal energy, entropy, and Gibbs energy as a function of pressure and temperature. Moreover, we were able to compare the values of these parameters for these two oxides, particularly within this field of study, which extends from the surface of the earth's crust to the confines of its outer core. We found that the results were in excellent agreement with previous studies. The MgO stabilizes in phase B1, while the dioxide transforms at a pressure of 59.2 GPa from this phase to phase B2. The agreement is also clear for the Debye temperature of both oxides, and the values of both the heat capacity with constant volume and the entropy at 300 K for magnesium oxide. While we were not able to compare the results of our calculation for both internal and free energy of oxides and the tow thermodynamic parameters for calcium oxide with the results of previous studies because they are not available.

phase transformation, Debye temperature, thermodynamic properties, MgO, CaO, PREM model